State investigators and smog regulators were at the massive, troubled ExxonMobil refinery in Torrance on Saturday to investigate why an 8-inch steam line ruptured and prompted a warning for residents to shelter in place and close their windows.

But 18 hours after the failure, ExxonMobil would not disclose what chemicals were in the giant cloud of steam seen pouring out of the plant at about 6 p.m. Friday.

“As a matter of practice, ExxonMobil does not comment on the details of day-to-day operations, the status of individual units or time lines of maintenance” ExxonMobil spokesman Todd Spitler said Saturday.

A specific question about what was released into the air was not answered. But the spokesman told City News Service the company is “working cooperatively” with state investigators “as we conduct our own investigation.”

State industrial safety experts from Cal/OSHA and investigators from the regional smog agency, the South Coast Air Quality Management District, were at the accident site, the latest in a string of catastrophic failures at the aging, huge refinery.

When the leak developed, nearby Crenshaw Boulevard was closed to traffic near 190th Street. Sirens warned neighbors to “shelter in place” out of what the nation’s largest oil company called “an abundance of caution.”

Spitler said ExxonMobil will share its findings with the Torrance Fire Department.

The leak was reported just before 6 p.m. Friday in the refinery’s crude unit, according to the Torrance Police and fire departments.

“The resulting leak resulted in a large column of smoke leaving the refinery and extending past Western Avenue,” according to a police statement.

The column was as much as 200 feet high, Torrance Fire Department Capt. Bob Millea said.

Sirens were activated to alert residents to shelter in place and close their windows, police said.

The leak was stabilized and contained and the “shelter in place” advisory was lifted at 6:50 p.m., Millea said.

No injuries were reported.

An ExxonMobil spokesman said the leaked substance was “mostly steam” but gave no indication of what else was released.

“In an abundance of caution, the refinery activated the Crenshaw Boulevard barriers and the Torrance Fire Department sounded the community warning sirens to alert the public to shelter in place,” Spitler said Friday. “The ‘all clear’ chimes were sounded minutes later.”

Refinery officials notified the state Office of Emergency Management Services and the SCAQMD about 6:30 p.m. Friday, he said.

“Air monitoring has been conducted in the community and there is no danger to public health,” he said. “We apologize for any inconvenience that this incident may have caused.”

In that case, ExxonMobil and the city reported that the leak, which began in the early morning hours and wasn’t stopped until that evening, wasn’t significant, but the Torrance Fire Department called it a “significant incident,” Bailey noted.